In refrigerated display cabinets which are provided with an access opening at the front side, air curtains are moved across the access opening of the cabinet to retain refrigeration. The characteristics of the air curtains are important to the efficient operation of the air circulation device. Such refrigerated display cabinets are well known and described in U.S. Pat. Nos. 3,134,243 and 2,862,369.
As disclosed in the above patents, the refrigerated display cabinet has a relatively large access opening exposed to the atmosphere yet must maintain its contents in a refrigerated state. The loss of refrigeration from the enclosed space through the access opening is reduced effectively by an air circulation device using a gaseous (preferably air) curtain which is continuously moved across the access opening from one edge to the opposite edge. The air curtain is formed by adjacent stream layers of air. The innermost stream layer is a refrigerated cold air stream; one or more outer stream layers or guard stream layers have temperatures approaching the ambient temperature. It is desirable to circulate the inner cold air stream and to circulate the adjacent guard stream layers to conserve the refrigeration and to maintain the enclosed space in a satisfactorily refrigerated state.
In these constructions of air circulating devices, assemblies including nozzles extend across the upper edge of the access opening and direct the air stream layer downwardly across the opening toward inlets which extend across the bottom edge of the access opening. Conventional air circulation devices use various methods to form the nozzle. Honeycomb materials have been used in the construction of such nozzles, since the plurality of air passages in the honeycomb create desirable flow characteristics. Honeycomb sections distribute the air in a more uniform fashion across the width of a nozzle. Such uniformity is desirable since it greatly reduces a tendency toward turbulence of the laminar air flow.
The honeycomb sections are normally assembled either as a plurality of plate elements or as a flat tube element having a plurality of air passageways therein. The former structure is complicated to assemble; many plate elements face each other with a gap and are bound by support elements on the outlet portion of the air circulation path. The latter structure is disclosed in Japanese Patent Publication No. 57-38253 in which a plurality of pairs of notched or scored lines are formed on opposite sides of a single flat tube. The lines are perpendicular to air passageways formed in the flat tube. The tube is bent along the notched lines and folded accordian style to form a honeycomb grid of a plurality of air passageways. However, because the honeycomb is formed by one flat tube, if the honeycomb is partially damaged during, e.g., the cleaning or replacing operations, the entire nozzle portion must be replaced.
Furthermore, turbulence-induced refrigeration losses impede the effectiveness of air curtains. Refrigeration losses can be attributed, to a substantial degree, to turbulence between moving air streams and adjacent still air. Specifically, the movement of a stream of air adjacent still air or adjacent another stream moving at a substantially different speed creates turbulence. The moving streams of air affected by turbulence periodically leave their intended paths causing large masses of the air to be removed and be unrecoverably lost from the circulating streams. Where these air masses are refrigerated, the load on the refrigerating means for the cabinet increases.
Moreover, the nozzle tube elements are normally formed of a synthetic resin, such as polyethylene or polypropylene, and each passageway is formed having a rectangular cross section with partition walls extending perpendicularly between two side surfaces of the tube elements. This renders the honeycomb section easily damagable from impacts with cleaning devices and during assembly and reassembly operations; impact forces against one side surface and directly transferred to the opposite side surface through the partition walls.